Traffic signals are installed at more than 312,500 intersections in the U.S. These signals are operated by connection to utility power lines. In the event of a power interruption, these signals become inoperative, creating a hazardous situation for vehicle operators and passengers. To alleviate this situation, an increasing number of major intersections have been equipped with backup power systems, typically capable of powering the signals for a few hours, while power is being restored, or temporary stop signs are erected.
A number of portable traffic signals have been designed, which might have use in such situations. However, a significant safety issue hampers their use. When power is restored to the system, timing of the temporary, portable devices does not match that of the permanently mounted signals. Even small differences in timing, over a period of minutes or hours, can result in conflicts where, for example, the permanent signal may be red in a given direction, while the portable signal shows green. It is easy to imagine the confusion this could cause, and the resulting accidents. Given the typical disruption that results when the power goes out, it could be hours or even days before a crew arrives to remove the portable signal.
The present invention describes a control system that resolves this conflict. During a power outage, a temporary traffic signal can function in response to timing commands from its own controller, maintaining order. However, when power is restored, the temporary signal timing is determined by data inputs from the permanently installed signal, with the result that both display identical indications, and change at the same time. As an option, if conditions warrant, data inputs from the permanently installed signal can be used to inhibit operation of the temporary signal.
Those of skill in the art will appreciate the present invention, which addresses the above problems and other significant problems, the solutions to which are discussed hereinafter.